Radio receiving system



July 16, 1929. v R. E.IDE LAND 1,721,146

RADIO RECEIVING SYSTEM Filed Aug. 31, 1927 2 Sheets-Sheet 1 My $56? (5 m??? July 16, 1929. R. E. DE LAND 1.721J

mo ancmvnm SYSTEM Filed Aug. 31, 1927 I2 Sheets-Sheet 2 til Patented July 16, 1929.

ROBERT E. DE LAND, or MILWAUKEEYWISGOZNSIN.

RADIO nncsrvme SYSTEM.

Application filed August 31,1927. Serial No. 216,676.

This inventionrelates to a radio receiving system.

In radio receiving, systems, it is a well known fact that the interelectrodal coupling furnished by the tube between the output and inputcircuits is such that a certain amount of energy is fed back from the output to the input circuit and the system is thrown into violent oscillation, particularly if an inductance, is employed in both the plate and in the grid circuit or other resonant means used Attempts have been made to correct this defect by neutralizing the coupling through the tube, but it has been found that these attempts are unsatisfactory, for it is apparent that the coupling through the tube is greater for the high frequencies and lesser for the low frequencies. The balancing due to the neutralizing action of the devices added, .must necessarily be where the. greatest feed back occurs, namely, at the highest frequencies, and consequently, the couplingbetween the output and the input circuit is too great for the lower frequencies, and the set does not therefore o-perate at anywhere near its maximum efficiency over the entire range of frequencies but itis most eflicient at one point only, and rapidly falls off as this point is passed. v

This invention is designed to overcome the defects enumerated above, and objects of this invention are to provide a novel form of radio receiving system inwhich equal amplification over the entire active band of frequencies is obtained, in which an auxiliary circuit is provided which causes a feed back of energy from the output to the input circuits in gradually increasing amounts as the frequencydecreases, and inswhich the total feed back due to the interelectrodal coupling and the action of the auxiliary circuit is constant andindependent of the frequency, or, in other words, to provide a'system in which the algebraic sum of the energy fed .back from the plate to the grid,;and the energy fed back due to the auxiliary circuit, is, of constant value. I In radio receiving systems as heretofore constructed, it-is a recognized fact that the type of coils or inductances used must be of the highest quality with the minimum of distributed capacity. This necessarily increases the cost of the'system. yThis invention, however, is designed coils :which have a high distributed capacity for the use of verycheap.

and, consequently, may be most cheaply constructed. The-system itself utilizes the very defects of these coils to improve the overall efficiency-of the set and to maintain constant amplification throughout the entire wave bandas will appear in the detailed description following.

Further objects are to produce a system which may be very cheaply constructed, which may be readily tuned by an unskilled operator without any chance of throwing the set into oscillation, and which is so made that the maximum amplification, without throwing the set into oscillation, is obtained. Embodiments of the invention are shown in the accompanying drawings in which:

Figure l is a diagrammatic view showing one form of the invention; 1

Figure 2 is aview showinganother form thereof; 1 r Figure 3 is amodification showing a different arrangement that may be. employed with the form shown in connection with Figure 2, for instance; 1 l

' Figure 4 is a further form of the invention. I V 7 Referring to Figure 1, it will be seen thata vacuumtube 1 has been illustrated as provided withthe usual plate 2, filament 3, and grid 4. The grid; circuit is tuned by means of the input coil 5- and variable condenser 6, or in anyother suitable manner. The

terminals of the tuned .inputcircuit are connected to the grid and filament. The-usual filament battery 7 is employed in connection with the filament controlling rheostat 8, if desired, and the usual B battery 9 is connected to the plate; This B battery is connected through a radio frequency choke; 10 and an output coil 11, such for instance, as

rarest emuthe primary of a radio frequency transformer. g a I I An auxiliary circuit has one end connected to the point between the coil 11am the choke 10. Its other end is connected through a coil 12 to the filament, or in other words, to one side of the coil5. The coils 12 and 5 are in inductive relation, whereas the radio frequency choke 10 and the coil '11. are not in-inductive relation. This auxiliary circuit includes a. radio frequency choke 13 and a condenser 14.

One specific'exampleof the values of-the radio frequency chokes maybe given, although it is to be distinctly understood that this is merely for the purpose of illustraner as limiting the invention.

has distributed capacity,

It is to'be noted that the poorlyconstr lct ed chokes have the same effect as parallel Iresonant circuits, as their distributed'capac- *ity-and inductance are in parallel. Consequently, at their-respective resonant frequenciesthey offer theoretically infinite impedance.

YAssume now that a signal is beingreceived in the low wave length range, or in other words, in the high frequency range. The coupling from the output circuit to the input circuit through the choke 13 and the condenser 14 is such that the energy flow .through this auxiliary-circuit issuppressed to a large degree, whereas the radio frequency. energy flow through the choke 10, is comparatively-free. This is due to the above noted fact that both the chokes 10 and 13 have considerable distributed capacity and also have resistance and inductance. They are not, therefore, sharply resonant at their resonant point, butinstead are broadly resonant; that is to say, the resonant curve has a peak, but it is not a sharp peak. It I gradually rises and thereafter gradually falls in the well known manner for a coil of this type.

'It is apparent therefore that Whenever the point of resonanceiof the coil 13 is approached that the energy flow through the auxiliary circuit is reducedto a marked degree and that as the frequency decreases,

the resonant point for the coil 10 is approached, and such coil tends to suppress radio frequency energy flow therethrough, whereas the coil 13 permits an increasing amount'to-pass. ,The net result of this is that as the frequency decreases, the choke 10 suppresses more and more of the radio frequency energy and the choke 18 bypasses more and more'of such energy.

It is apparent that the condenser let may be-made variable, if desired, and may be adjusted for each set and thereafter fixed, determining the exact amount of energy fed large bypass condenserv 15 may be bridged around the batteries 7 and 9. The radio frequency energy fed back is fed into the grid circuit or input circuit in gradually increasing amounts as the frequency decreases, or, in other words, as the wave lengthincreases. It is apparent, therefore,that the-coupling between the output and input circuit is so made that the algebraicsuinjof the energy fed back through the is wholly indepen The choke coil 13 in-the auxiliary,

formers for any given frequency, If desired, a

interelectrodal coupling 'ofthe tube and through the auxiliary circuit is constant, and cut of the frequency. Thus, the circuit maybe adjusted for the maximum amplification possible without throwingthe set into violent oscillation, and this relation will be maintained throughout the active band of radio frequencies for which the system is designed. The system, therefore, secures-a constant amplification at all frequencies. There is, therefore, no falling off in amplification, aseither end of the wave band is approached. The maximum output, therefore, or in ;other words, the maximum overall 'efii'ciency, is obtained by this system.

It is to be noted'particularly-that inasmuch as the radio frequency choke coils 10 and 13 are intended to be broadly resonant as distinguished from" sharply resonant, that therefore cheap coils may be employed, which couldnot hithertofore be'succes'sfully used with the ordinary'types of radio frequency amplifying sets. This very marked'ly reduces the cost of the system and also facilitates its production, for it is well known that the radio frequency chokes which have considerable distributed capacity and resistance, may be formed in a very compact manner, as no especial care is needed in their construction. r r

It is clear also that the condenser 14 may be either fixed or variable. The condenser afterit 'has once been set, is left fixed o throughout the entire operation of the set. Clearly, therefore, fixed condensers could be used, as well as variable ones=for the condenser 14.

The system shown in Figure 2 discloses a plurality of stages which operate on the general principle disclosed in connection with Figure'l. However, this system differs from Figure 1 in that the inputand output transgiven tube in thesystem consist of a primary 16, asecondary 17, and an auxiliary coil 18. The coils 18 are connected through a radio frequency choke 19 having resistance, distributedcapacity, and inductance, and through a condenser 20. If desired, these coils may be connected in a continuous circuit from one end of the system to the other, as shownin Figure 2. The otherend of each of the coils 18 is'connected to the filament busbar 21. In other words, the coils 18 supply energy whichis transferred from the output circuit to the input circuit through the medium of the radio frequency choke 19 and the condenser 20. .If

esired, the condensers 20 may be omitted resonate at 150 meters. 'It is to be noted that 5 the coil '19. hasidistribute'd capacity, inductance, and resistance and therefore acts as a parallel resonant circuit and offers, theoretically, infinite impedance at its resonant frequency. Consequently, the feed back increases as the frequency decreases. parent also that the choke coil may be bridged by the condenser, if desired, as shown in Figure 3, in which the choke coil 19 is bridged by the condenser 20.

In the form shown in Figure 3, the choke 19 and condenser 20, may have a resonant period jointly at approximately 150 meters, so that at this frequency the auxiliary circuit offers infinite impedance to the passage of radio frequency energy. However, as the frequency decreases and the Wave length increases, more and more energy will be permitted to pass.

In the form shownin Figure 4, another method is employed to secure the results heretofore enumerated. In this form of the invention, the input circuit includes the coil 22 and variable condenser 23 which are connected to the grid and filament. The plate is connected through the output coil 24 to the B battery 25. A radio frequency choke 26 is connected through a condenser 27 directly between the plate and filament circuits.

A specific example used as illustrative only and not limiting may be given for this circuit. In the ordinary range of broad.- casting frequencies, the radio frequency choke 26 may resonate at 550 meters. This radio frequency choke, similar to those previously described, has distributed capacity, inductance, and resistance, and is not sharply resonant, but is broadly resonant, so that as the critical frequency is approached, more and more retardation to the passage of radio frequency energy is offered, and as the critical frequency is departed from, less and less retardation of the passage of radio frequency energy is produced. Consider, for example, the operation of the systern when receiving signals. When the fre-v quency is .relatively high, the bypass directly between the filament and plate bypasses a large amount of the radio frequency energy and as the frequency decreases and the wave length increases, the radio frequency choke ofiers greater and greater retarding action to the radio frequency energy and, consequently, increases the energy flowing through the tube due to interelectrodal coupling between the output and the input circuits. effect of this coil is to force more and more radio frequency energy back to the input It is ap- In other words, the

circuit as the frequency decreases and :to

bypass more and more of the radio frequency energy as the frequency increases. It also gradually increases the radio frequency energy flow through the, coil. 24 as the frequency decreases.

It is to be noted that in all forms ofthe invention the radio frequency chokes may be bridged by condensers in order to form parallel resonant circuits. However, as previously described, the poorly constructed radio frequency chokes really have sufficient distributed capacity to. produce a parallel resonant circuit and these condensers are not ordinarily needed; g

It will be seen, therefore, that a system of radio frequency amplification has been dis closed which gives an equal amplification throughout the entire band of wave lengths for which the system is designed.

Also, it is to be noted particularly that with this system, very cheap andpoorly constructed radio frequency chokes may be used as their relatively high distributed capacity and resistance does not detract from their is utilized to produce, the broadly resonant V effect. This result may be enhanced by using resistance wire for the chokes, if desired.

Although the invention has been described in considerable detail, such description is intended as illustrative rather than limiting as the invention may be variously embodied and as the scope of such invention is to be determined as; claimed.

I claim: y A radio receiving system comprising a vacuum tube having a grid, a filament and a plate, a coil connected to said plate and constituting an output element, a coil connected to said grid and constituting an input element, a pair of coils inductively related to the input and output elements and connected through a radio frequency choke and a condenser. I

In testimony that I claim the foregoing I have hereunto set my hand at Milwaukee,

in the county of Milwaukee and State of Wisconsin.

ROBERT E. DE LAND. 

